1. Field of the Invention
This invention relates to a camera, with a distance-measuring sensor unit, for use in a photogrammetric analytical measurement.
2. Description of the Related Art
For example, photogrammetry is carried out at a traffic accident spot. The traffic accident spot is photographed by a camera in at least two different locations, and a set of photographed pictures is selected to establish a survey map of the traffic accident spot.
In particular, a two-dimensional coordinate system is defined on each of the photographed pictures, and two-dimensional positions of objects, which are recorded on each picture, are determined in accordance with the two-dimensional system. Then, a three-dimensional coordinate system is produced based on the two sets of two-dimensional coordinate systems, and three-dimensional positions of the recorded objects are determined in accordance with the three-dimensional coordinate system. Accordingly, it is possible to obtain a survey map of the traffic accident spot by drawing the objects on a sheet of paper such that the objects are projected on one of the three planes defined by the three-dimensional system.
Before accurately scaled distances and lengths can be reproduced on the survey map, a standard measurement scale must be recorded together with the objects in the photographed pictures. Also, a standard reference plane, on which the survey map should be based, must be defined in the photographed pictures.
Usually, in order to define the standard measurement scale and the reference plane, three respective cone-shaped markers, which are identical to each other, are positioned at suitable locations of a traffic accident spot. Namely, a distance between two apexes of the cone-shaped markers, measured, for example, with a measuring tape, is defined as being the standard measurement scale, and a plane, defined by the three apexes of the cone-shaped markers, is utilized as the reference plane.
If the ground is flat at the traffic accident spot, i.e. if the reference plane, defined by the apexes of the markers, coincides with a horizontal plane, it is possible to properly and precisely draw the survey map on the reference plane. However, if a surface of the ground is sloping, i.e. if the reference plane is inclined with respect to the horizontal plane, the survey map cannot be properly and precisely drawn.
Accordingly, when the ground surface is sloping, a slope angle must be measured and the determination of the three-dimensional positions of the objects should be carried out, taking the measured slope angle into consideration, before a proper and precise drawing of the survey map can be ensured. Nevertheless, it is troublesome to measure a slope angle of the ground surface, and the measurement of the slope angle may be mistakenly not taken into account.
On the other hand, there is also a demand for drawing a survey map on a vertical plane, perpendicular to the horizontal plane or the reference plane. Before this demand can be satisfied, a vertical distance between the camera and the ground surface should be measured. Similarly, it is troublesome to measure such a vertical distance between the camera and the ground surface, and the measurement of the vertical distance may also be mistakenly not taken account.